The present invention relates to a process for preparing di-tertiary-peroxides, derived from the cumene hydroperoxide.
More specifically the present invention allows to have improved yields in the dicumylperoxide preparation process.
The condensation reaction between cumene hydroperoxide and alcohols with formation of di-tertiary-alkyl-aryl peroxides in the presence of acids as catalysts, is known in the prior art. Specifically, for the dicumyl peroxide preparation, cumene hydroperoxide and xcex1-cumyl alcohol in the presence of more or less strong acid as catalysts are used.
The following processes for the dicumylperoxide production starting from cumene hydroperoxide and xcex1-cumyl alcohol are known in the prior art.
Processes wherein a strong acid as sulphuric acid, methionic acid, toluene sulphonic acid, is used as catalyst in the reaction system. Other processes in which the same acids are used as catalysts and in which water is removed from the reaction mixture by distillation at reduced pressure and/or by addition of a volatile inert organic liquid (see G.B. 896,813).
Another process wherein as catalyst a strong acid of the above mentioned type is used, characterized in that the reaction is carried out in the presence of one or more polar solvents and the water formed during the reaction is continuously removed from the reaction system (see U.S. Pat. No. 4,413,148).
In another process oxalic anhydride is used in the reaction as acid catalyst and dehydrating agent (see U.S. Pat. No. 4,413,148).
Finally a process wherein a weak acid as potassium bi-sulphate is used as catalyst and wherein an inactive gas is continuously fed in the reaction system (see U.S. Pat. No. 4,413,148).
When a strong acid is used as catalyst the reaction must be carried out under restrictive conditions since both cumene hydroperoxide and dicumylperoxide are easily decomposed by the strong acid and it is necessary to select in an optimal way both the catalyst use amount and the reaction temperature; in general under the reaction conditions used in the above mentioned patents of the prior art, the process gives rather low yields.
Other meaningful drawbacks connected to the use of acid catalysts of the prior art in this process are the production of meaningful amounts of by-products and the reaction control difficulties and consequent safety problems.
The acid catalysts used in the prior art comprise both inorganic acids such as sulphuric acid, hydrochloric acid, perchloric acid and the like, and organic acids, such as para toluen sulphonic acid, methionic acid, trichloroacetic acid and the like.
One of the technical problems derived from the use of the sulphuric acid is the production of meaningful amounts of by-products, such as phenol, acetone, xcex1 methyl styrene, dimers of the xcex1 methyl styrene and others, with low yields and safety problems.
The use of the para-toluensulphonic acid shows advantages with respect to the sulphuric acid, improving the reaction yields and giving rise to a more controllable reaction.
The Applicant has surprisingly found a process to produce di-tertiary-peroxides, specifically dicumylperoxide, by reacting a tertiary-hydroperoxide with a tertiary-alcohol in the presence of a specific catalyst which allows, compared with the acid catalysts of the prior art, to further improve the reaction yields, by a by-product reduction.
It is therefore an object of the present invention a process for the synthesis of di-tertiary-peroxides, specifically dicumylperoxide, wherein the condensation reaction between a tertiary-hydroperoxide and a ter-alcohol is carried out in the presence of an acid catalyst, formed of a compound having a mono-sulphonated aromatic ring selected from the following formulae: 
wherein: R is an alkyl group having from 2 to 9 carbon atoms, preferably from 2 to 6; Rxe2x80x2 and Rxe2x80x3 are alkyl groups having from 1 to 9 carbon atoms, preferably from 1 to 6.
Preferably the molar ratio between the tertiry-hydroperoxide and the tertiary-alcohol has a value in the range 0.9-1.2.
The acid catalyst is used in a percentage by weight in the range 10%-40% with respect to the reacting organic mixture.
The reaction can be carried out in a reactor wherein the acid catalyst of the present invention is gradually introduced inside the reaction system so that the reaction temperature is in the range 25xc2x0-60xc2x0 C.
The reaction mass is maintained under stirring for about 30-90 minutes, at the end the acid aqueous phase is separated and the organic phase is recovered.
The product is characterized at the end of the condensation reaction, by gaschromatographic analysis (High Resolution Gas Chromatography HRGC) in order to evaluate the peroxide and the by-product content.
Subsequently the organic phase is washed with an alkaline solution to remove the phenol and the cumene hydroperoxide present in the reaction product. Then a washing is carried out with an aqueous solution to eliminate the residual alkalinity.
When the washings are over, the organic phase is subsequently purified by subjecting it to a stripping treatment in vapour counter-current to eliminate the volatile organic components.
At the end the product is anhydrified and characterized in terms of iodometric and gaschromatographic analysis titre with internal standard (titre higher than 98%).
Specifically the invention process is applicable for the dicumylperoxide preparation by reaction between cumene hydroperoxide and xcex1-cumyl alcohol.
One of the main uses of the invention di-tertiary-peroxides is as polymer curing agent (e.g. PE, EPR etc.).